Floating rust preventing film coated steel members for buildings and structures

ABSTRACT

Steel members, particularly weatherproof low alloy steels for use in buildings and structures, the surface of said steels being coated with a film containing an oxide pigment mainly composed of manganese dioxide and the rest being a film forming composition for the purpose of preventing the formation of an undesirable floating rust on said surface while promoting the formation of a stable hard protective rust on said steel surface.

United States Patent [191 Watanabe et a1.

1451 Apr. 15, 1975 [22] Filed:

[ 1 FLOATING RUST PREVENTING FILM COATED STEEL MEMBERS FOR BUILDINGS ANDSTRUCTURES [76] Inventors: Shozo Watanabe, 12-66,

Komatsu-cho, Hirohata-ku; Minoru Kitayama, 3-29, Azuma-cho, Horohata-ku;Shigenori Yamadera, 32, Kitagawara-cho, Hirohata-ku; Yasuyuki Taniguchi,14, Katsuhara-cho, Katsuhara-ku; Susumu Yamaguchi, 4-85, Kamiya-cho, allof l-limeji, Japan May 6, 1974 211 App]. No.: 467,566

Related US. Application Data [63] Continuation-in-part of Ser. No.197,440, Nov. 10,

1971, abandoned.

[52] US. Cl 428/336; 148/6.14 R; 148/315;

428/458; 428/461; 428/463; 428/472 [51] Int. Cl B32b 15/08; B44111 1/36[58] Field of Search 117/132 B, 132 C, 133,

117/161 K, 161 UZ, 161 UC, 161 UP, 162; 148/6.14R,31.5

[56] References Cited UNITED STATES PATENTS 2,148,862 2/1939 Kern117/132 C 2,238,651 4/1941 Kcencn.... 106/14 UX 3,249,447 5/1966 Higgins106/14 3,502,512 3/1970 Bigos et a1. 148/635 3,617,364 11/1971 Jarema117/132 BE FOREIGN PATENTS OR APPLICATIONS 712,902 8/1954 United Kingdom252/387 OTHER PUBLICATIONS Belyi et a1., Chem. Abs. Vol. 72, No. 15285g,Jan. 1970.

Maksimov et al., Chem. Abs. V01. 68, No. 62070k,

Primary Examinerl-1arry J. Gwinnell Attorney, Agent, or FirmWenderoth,Lind & Ponack [57] ABSTRACT Steel members, particularly weatherproof lowalloy steels for use in buildings and structures, the surface of saidsteels being coated with a film containing an oxide pigment mainlycomposed of manganese dioxide and the rest being a film formingcomposition for the purpose of preventing the formation of anundesirable floating rust on said surface while promoting the formationof a stable hard protective rust on said steel surface.

5 Claims, 3 Drawing Figures PATENTEUAPR 1 51975 3,877,

SHEET 1 BF 2 PIIIEI-ITEIIIPR I 5I975 3,877. 977

SIIEEIEIIfZ VARIATION IN THE OUTFLOW OF F6 WITH THE LAPSE OF TIME I NIgIG L RUST INITIAL FLOATING 6O RUST FORMATION F K FORMATION Q ALPHABETSARE SIGNS OF SAMPLE S OUTFLOW AMOUNT OF Fe (mg/IOOm I.)

f UNTREATEO IBBARE) STEEL MEM ER 0 I I I -5 8I0 0 ;E OV R 8% I-Ti/ I I II 3 6 9 Q I8 2I 24 27 3o 33 36' INVENTOR s EXPOSURE TEST RERIOO (INMONTHS SHOZO WATANABEI MINORU KITAYAMA, SHIGENORI YAMADERA, Fl YASUYUKITANIGUCHI AND SUSUMU YAMAGUCHI BYIDQAIIIMM W \LPMOIL ATTORNEY FLOATINGRUST PREVENTING FILM COATED STEEL MEMBERS FOR BUILDINGS AND STRUCTURESThis is a continuation-in-part of US. application, Ser. No. 197,440,filed Nov. l0, I971, now abandoned.

The present invention is directed to the production of steel memberscoated with a floating rust preventing film to be used for buildings andstructures. and more particularly to a weatherprooflow alloy steel to beused for buildings and structures. This low alloy steel is such that itprevents the formation of a floating rust ordinarily formed whenconventionally used weatherproof low alloy steels are exposed to theatmosphere. At the same time, the weatherproof low alloy steels of thepresent invention are such as to promote the formation of a stable rust.

lt is well known that a weatherproof low alloy steel has suchproperties, that, when it is exposed to the atmosphere, there isobtained the formation of a hard compact film or rust on the surface ofsaid steel after the lapse of several years, whereby subsequentcorrosion may be prevented. Thus, as the weatherproof low alloy steelshows a weatherproofness several times that of ordinary steel, it isextensively adopted for use in buildings and structures which areparticularly exposed to the atmosphere. However, this weatherproof lowalloy steel has a shortcoming in that an undesirable yellowish brownrust (which shall be called a floating rust hereinafter) is formedthereupon before the abovementioned hard compact protective rust isformed. Such a floating rust causes various problems in that it flowseasily out of the steel surface or peels off after the steel members arepiled, thereby not only causing a wasteful consumption of the steelmembers but also staining the surrounding of buildings and structuresmade of these steel members.

An object of the present invention is to solve the various troublescaused by the generation of floating rust while at the same timepromoting the formation of a hard compact protective rust on the surfaceof the steel. 7

The above-mentioned object is attained fundamentally by the followingsubject matter according to the present invention.

The said object of the present invention can be achieved by coating thesurface ofa-weatherproof low alloy steel with a film consisting of anoxide pigment, including manganese dioxide, and a film formingcomponent. In this case, it is immaterial whether the film may be formedon the steel surface in the step before or after the steel member isassembled in a structure or building.

FIG. 1 is a photograph showingthe, state of a steel member being stainedin the surroundings and consumed by the outflow ofa floatingrustproduced before a stable rust was formed when a bare weatherproof lowalloy steel was exposed to the atmosphere.

FIG. 2 is a photograph showing the surface state when a weatherproof lowalloy steel treated according to the present invention was exposed tothe atmosphere for about 9 months.

H65. 3 and 4 are photographs showing states of a compact stable rustformed on a steel surface after the lapse of about months and about 18months respectively, when a weatherproof low alloy steel treatedaccording to the present invention was exposed to the atmosphere.

FIG. 5 is a graph showing the variation ofthe amount of iron flowing outof the surface of a sample during an exposure test period.

The floating rust preventing film according to the present inventionconsists of an oxide pigment, including manganese dioxide, and a filmforming component so that, when a weatherproof low alloy steel is coatedon the surface with such film (which shall be called a floating rustpreventing film hereinafter), water may be inhibited from penetratingthe surface ground of the steel from outside by the action of the filmforming component. The oxide pigment contained in the film, on the otherhand, forms a bridge for oxygen in a stable rust accelerating filmwhile, at the same time, acting as a carrier for oxygen due to thecatalytic action of the manganese dioxide contained in the same film.whereby oxygen may be fed in turn to the steel surface ground fromoutside through the film.

When the weather proof low alloy steel coated with a floating rustpreventing film, which has such operating mechanism as abovementioned,is exposed to the atmosphere, the oxidation of the steel surface groundbelow the floating rust preventing film is accelerated without passingthrough the process of an ordinary wet corrosion, that is, withoutundergoing the formation of a floating rust, because active oxygen (inan atomic form) is fed to the steel surface ground through the film. Thepenetration of water into the steel surface ground is, however, kept toa minimum by the action of the film forming component (vehicle).Moreover, because the stable rust produced on the steel ground surfaceis incorporated with a part ofthe oxide pigment contained in thefloating rust preventing film, said stable rust becomes more compact.whereby the progress of corrosion is restrained without undergoing theformation of the floating rust.

This stable rust shows, for example, a blackish brown or dark browncolor, is compact and hard. and has a sufficient weatherproofness.Therefore, it has a performance comparable to that of an ordinary stablerust formed on the surface of a bare weatherproof low alloy steel, whichhas been exposed to the atmosphere for 4 to 5 years and, after thefloating rust preventing film has been peeled by weathering, the stablerust exhibits a corrosion preventing effect.

In such case, all the oxide pigment can be made of manganese dioxideonly, but in order to improve the tone of the floating rust preventingfilm, it is desirable to use an oxide pigment consisting of manganesedioxide and one or more of such other oxide pigments as are selectedfrom among for example, iron oxide, copper oxide, titanium oxide andlead oxide. In such case, however, it is necessary that the amount ofmanganese dioxide should be at least l% and that the oxide pigmentincluding manganese dioxide should be 30%, When the oxide pigment isless than 30%, a bridge for feeding sufficient oxygen to the steelsurface ground is scarcely formed in the floating rust preventing film.On the other hand, any oxide pigments other than manganese dioxide areso weak in oxygen carrying capacity that they do not form a stable ruston the steel surface ground. However, if at least 1% manganese dioxideis contained, the oxygen carrying capacity is remarkably elevated by itscatalytic action and a stable rust can be formed on the steel surfaceground, while a floating rust preventing film is still present on thesteel surface.

From the viewpoint of the oxygen carrying capacity, the upper limit ofthe amount of the oxide pigment is desirably high. However, if thecontent thereof is too high, there are many disadvantages in that thespray nozzles are clogged at the time when the stable rust film is beingformed and the stickness and adhesiveness of the film are reduced. Inview of these facts,'therefore; the upper limit value of the oxidepigment is desirably about 70%.

Next, the thickness of such floating rust preventing film shall beexplained. The thickness of the film is intimately related to itsperformance and life. If the film is too thin, there are produced suchfilm defects as pinholes and painting irregularities. Further, anordinary wet corrosion is produced on the steel ground surface as wellas a stable rust and a floating rust. On the other hand, if the filmthickness is too large, there occurs a shrinking phenomenon in the film.When taking such defects and the coarseness of the surface to be paintedinto consideration. the thickness of the floating rust preventing filmis preferably about to 70 ,u.

The film forming component to be used as the base of the floatingrust-preventing film of the present invention is required to be capableof forming a film during the lapse of 2 or 3 years, after it has closelyadhered to the surface of a weatherproof low alloy steel, while holdingparticlesof the above mentioned oxide pigments dispersed in the film. I

The film forming component of the present invention must exhibit thefollowing characteristics in order to meet the above mentionedrequirement.

First, the film forming component of the present invention is requiredto be waterproof. Further, it is required to have the property ofdry-hardening at a normal temperature (a thermo-hardening property isnot practical because the film is to be applied to buildings andstructures, according to the present invention. Still further, the filmforming component must have excellent adhesiveness to the descaledsurface of the weatherproof low alloy steel, as the film must be held onthe surface of steel materials for use in buildings and structures. andalso, the film must be adhesive so as not to peel off when the steelmaterials are assembled and worked.

Since the floating rust preventing film of the present invention shouldbe replaced by a stable rust formed under the said film after a lapse of2 or 3 years, the film forming component is not required to have adurability of more than 3 years to exposure in the atmosphere; rather itis preferable that the film be weathered after a lapse of 2 or 3 years.a

As a result of the inventors search for materials satisfying the abovementioned requirements, it has been discovered that organic resins suchas alkyd resins (particularly, oil-modified alkyd resins and styrenatedalkyd resins), acrylic resins (particularly, acrylic resins of theemulsion type), phthalic acid ester resins, and cumarone resins, andrubber derivatives such as cyclized rubber, rubber chloride andpolyalkylene sulfide resins (Thiokol) are suited to the use as a filmforming component which possesses the waterproofness, dry hardeningproperty at normal temperature and close adhesiveness to the steel asabove mentioned.

Specific examples of the resins contemplated in the present inventionwill be described below.

Acrylic Acid Ester Resins These are resins obtained by thecopolymerization of acrylates under the action of a catalyzer such asbenzoyl peroxide and the, like, said acrylates having carbon atomsusually within the range of 1-4 in the alkyl group, forming the estermoiety (i.e. the residual alcohol group) with the acrylic acid.

The physical and chemical properties and the trade name of the acrylicacid ester resin used in the experiments of the present invention are asfollows:

Specific gravity 1.3 l.5

Tensile strength (kg/cm) l00 l 10 Elongation (/z) 400 500 Modulus ofelasticity ltlkg/cm") I 220 Water-absorbing percentage (Dipping for 24hours) (7:) 0.3 0.4

Viscosity (of 25% toluene solution at 25C) (Stokes) 3 4 Dipping in l071H 80, at 25C X 240 hrs. Swelling Dipping in 10% NaOH at 25C X 240 hrs.Swelling Additive No addition Trade name (Manufacturer) Alon S 1002 (TOAGOSEl CO..

Japan) Tensile strength (kg/cm") 425 490 Elongation (71) 1.5 2.5

Modulus of elasticity (l()'kg.cm"') 3 3.5

Water-absorbing percentage (Dipping for 24 hrs) (/1) 0.03 0.04

Viscosity (of 25% toluene solution at 25C) (Stokes) 4 5 Dipping in 10% Hat 25C 240 hrs. No change Dipping in 107: NaOH at 25C X 240 hrs. Nochange Additive Not known Trade name (Manufacturer) Styren 666(ASAHl-DOW CO" Japan) Phthalic Acid Ester Resins This is an oil-modifiedalkyd prepared by modifying a condensate of phthalic anhydride andglycerine by soya bean oil. This resin is composed of 24-26% phthalicanhydride 54-58% of an oil substance and is used as a conventionalvarnish. Naphthene lead is added as an additive prior to the'use of theresin.

The physical and chemical properties as well as the trade name of theresin used in the experiments of the present invention areas follows:

Specific gravity l.0l l.2() Tensile strength (kg/cm") 70 Elongation 1I60 210 Water-absorbing percentage (Dipping for 24 hrs) ('71) 0.06 0.09

-Continued Viscosity (4571 dissolved as nonvolatile matter in toluene)(Stokes) 12.5-14.0 Dipping in l07r H SO at 25C X 240 hrs. No changeDipping in NaOH at C X 240 hrs. Slightly corroded Additive (Naphthenelead) Trade name (Manufacturer) 0.4 0.6 (as lead) Phthalic acid resinwhich is a vehicle of "TAlKO-MARINE" of DAl NIPPON TORYO. CO. (Japan)\\'as used.

Cumarone Resins These resins are obtained by polymerizing a hydrocarbonoil, which has a boiling point range of 130-200C in respect to relatedcoal dry distillation components. at 40-l20C under the existence of aFriedel-Crafts type catalyzer.

This resin has the following physical and chemical properties. Theresin. however. used in Applicants experiments was self-manufactured.

V type Cumaron resin (NIPPON STEEL CO.)

Trade name (Manufacturer) Cyclized Rubber This is an isomer of naturalrubber and is a rcsino'td obtained by cyclizing natural rubber by meansof the action of stannic chloride.

The physical and chemical properties and the trade name of the rubberused in the experiments of the present invention are as follows:

Specific gravity 1.0 l.l

Refractive index nD 1.542 1.546 Chlorine part (71) 1.5 1.7 lodo value180:10 Water-absorbing percentage (Dipping for 24 hrs) (/11 0.04 0.05Viscosity (of 25% toluene solution at 25C) (Stokes) 3.5 4.5 Dipping in1071 H 50, at 25C for 240 hrs. No change Dipping in [U /1 NaOH at 25Cfor 240 hrs. No change THERMOLlTE P (SEIKO KAGAKL' CO.. Japan) Tradename (Manufacturer) Rubber Chloride Specific gravity 1.5 1.7 Refractiveindex nN l.55 l-l.555 Tensile strength (kg/cm") 300-400 Elongation (7r 34 Water-absorbing capacity (Dipping for 24 hrs) (/11 0.2 0.3 Viscosity(of 25% toluene solution at 25C (Stokes) 3 4 Dipping in 1092 H 50, at25C x 240 hrs. No change Dipping in 1071 NaOH at 25C X 240 hrs. Nochange ALLOPRENE R 20 Trade name (l.C.l. CO.. England) PolyalkyleneSulfide This is a rubber of the polysulfide series produced by thecondensation ofa symmetrical alkyl dihalide and an alkali polysulfidesuch as sodium polysulfide. and is known under the trade name ofThiokol.

The physical and chemical properties as well as the trade name of thisrubber used in the experiments of the present invention are as follows:

Specific gravity 1.2 1.3 Average molecular weight 5000 6000 PropertiesSticky fluid at room temperature Viscosity (27C) 350 450 poises Mutualsolubility with various solvents Very good solubility with toluene.chlorobenzene and cyclohexan at any ratio.

Fairly good mutual solubility with methylethyl ketone. carbontetrachloride and the like.

Bad mutual solubility with methanol.

kerosene and the like. "THIOKOL" P 2 (THlOKOL CHEMICAL CO.. USA.)

Trade name When using this rubber as a film-forming component. leaddioxide is used as a hardening agent.

A paste-formed hardening agent supplied by the THl- OKOL CHEMICAL CO. asan addition agent is admixed at a ratio of 7.5 wt. parts to wt. parts ofthe LP 2.

Conventional paint films generally applied to steel members are mostlyto prevent rusting. For this purpose there is preferably used a filmcomposed of a paint-film forming component (vehicle) for preventing thepenetration of water and gases (air and corrosive gases) and pigmentswhich function as an inhibitor as, for example. lead oxide. red leadoxide (Pb- 0 or zinc chromate. However. when conventional rustpreventing paint is applied to the surface of a weatherproof low alloysteel, and the painted steel is exposed to the atmosphere. the rustingof said steel is indeed inhibited. However. after several years ofexposure to the elements. a floating rust is produced on the surface ofthe steel. Thus. the conventional paint films only serve to delay thegeneration of the floating rust.

According to the present invention. it is very advantageous toincorporate sulfur (S) into the floating rust prevention film. Such S isderived from such sources as sulfur. sulfur compounds and sulfuroussubstances. and one or more of these substances can be used herein. Itis well known that S is an element which accelerates corrosion. However.as a result of making exposure tests of many weatherproof low alloysteels and investigating floating rust preventing films for many yearsthe present inventors have discovered that- S. which has been heretoforeconsidered to be a detrimental element in that it accelerates corrosionand oxidation. may contribute greatly to the formation of a compactstable rust. and this is effected by the reaction ofS contained in thefloating rust preventing film with the steel ground surface. In suchcase. more than 0.05% S is preferably used in the floating rustpreventing film and may be used in theform of at least one substanceselected from sulfur. sulfur compounds and sulfurous substances. Thatis. when the S content is less than 0.05%. there is found substantiallyno effect as a result of the addition of S. in that the films are thesame as if no S had been added. On the other hand. if the S content ismore than 0.05% a more compact'stable rust is formed much earlier thanin the use of a floating rust preventing film which contains no S.However. if the S content is excessive. the weldability of the steel isimpaired and the film forming solution itself is deteriorated. From thispoint of view. the upper limit of the S tive amounts. said solutionsbeing prepared by using a normal-temperature dry type acrylic esterresin as a vehicle (specific gravity: 1.4; viscosity: 3.4 stokes-(2571toluene solution at 25C); trade name: Alon S 1002).

The results shown in the table and figure are obtained by applying saidsolutions on the surfaces of test pieces of weatherproof low alloy steel(composed of 0.087: C. 0.42% Si. 0.37% Mn. 0.094% P, 0.041% S, 0.20% Ni.0.30% Cu and 0.60% Cr. 50 X 150mm and a thickness of 3.2mm) descaled byshot blasting in thickness of 25 to 30 ,u.. and exposing thethus-obtained film to the atmosphere. Table 1, shows the time when astable rust was formed on the surface of the exposed piece and the stateof the steel surface ground at that time. FIG. shows the variation ofthe amount of iron flowing out of the sample surface during the exposuretest period..

as already mentioned. The so called outflow iron amount designatesvalues obtained by an analysis on the amount of Fe flowing out intowater flowing down on the surface of the sample. This is achieved byspraying deionized water on the surface of said sample at fixedintervals. 1

Table 1 Pigment in "/1 Time (in months) Surface state at the SampleOxide pigment in '71 Ebonite Total when a stable rust time mentioned onthe Manganese Black iron Total powder in was formed on left No. dioxideoxide is /l of S the steel surface A l 19 20 0 20 No stable rustYellowish brown floatwas formed ing rust 13 0.5 29.5 0 30 ditto ditto C1 29 30 0 30 24 Dark brown stable rust D 18 12 30 0 30 28 ditto E 1 2930 0.04 (0.01 30.04 24 ditto F 1 29 30 0.2 (0.05) 30.2 21 Blackish brownstable rust G 24 16 40 20 5.0) 60 15 ditto H 0.5 59.5 60 0 60 No stablerust Yellowish brown floatwas formed ing rust 1 l 59 60 0 60 24 Darkbrown stable rust 1 30 30 6t) 0 60 18 dim K 1 59 60 0.2 (0.05) 60.2 22Blackish brown stable rust L 30 30 60 0.4 (0.1 60.4 16 ditto content ispreferably 10% and the optimum range is 0.1

As evident also from Tablel and FIG. 5, it is necesto 5%. For theabove-mentioned sulfur compounds. sary that manganese dioxide should bemore than 171 there can be used such compounds as sulfates and sulfldesas. for example. CaSO NiSO ZnSO and CuS, and such organic sulfurcompounds as ebonite powder, factis and balsam sulfide.

The following shows the result of experiments carried out by theinventors.

and that the dioxide pigments including said manganese dioxide should be30%. In case these conditions are not satisfied. there is formed afloating rust. 1f the S to be contained in the film is less than 0.05%.the reaction for producing a compact oxide film rust is not accelerated,and the effect of adding S is not recognized.

Concrete examples of the weatherproof low alloy steel as the object tobe achieved by the present invention are shown in Table 2. however. theinvention is not limited to them.

Table 2 Refer- Chemical composition in 7:

ence C Si Mn P S Cu Cr Ni V Ti Mo Ni a. 1 $0.12 0.25-0.75 0.20-0.500.07-0.15 0.035 0.25-0.55 0.30-1.25 0.65 b. 2 0.10-0.19 0.15-0.300.70-1.25 $0.035 $0.035 0.25-0.40 0.40-0.70 0.02-0.10 c. 3 0. I 20.25-0.75 1.20 0035-0. 1 2 0.035 0.25-0.50 0.40-10 0.65 0.15 d. 4 0.180.35 1.4 0.04 0.04 0.25-0.4 (1.20-0.50 I e. 5 $0.12 $0.60 50.600.06-0.12 S 0.04 0.2-0.5 0.4 -1.2 $0.35 f. 6 $0.18 S0.55 51.20 50.040 50.04 0.20-0.50 0.4 -1.20 $0.10 50.35 50.10

Table 2-Continued Chemical composition in 7: Refer- J y t ence C Si Mn PS Cu Cr Ni V T i Mo N:

g. 7 0.15 0.10am filo 5.0.15 0.03, 0.3-0.6 51 $0.65 0.10 0.20 r h. 850.]5 $0.60 (lJll-l .0 50.110 0.04 (LI-0.50 0.3041 50.50 T 0.10

a. CORTEN o Concrete examples shall be explained in the following:

l. Chemical composition of the used weatherproof low alloy steel:

0.01071 0.4071 Si. 0.38% Mn. 0.090% P.

0.0l77r S. 0.18% Ni. 0.28% Cu and 0.59% Cr.

2. Composition of solutions for forming floating rust preventing film:

Acrylic ester resin (specific gravity: L4; viscosity: 3.4 stokes (259itoluene solution at 25C: trade name: Alon S 1002) of normal temperaturedry type 4092 by weight a) Manganese dioxide l-l'lr by weight Iron oxide(mixed iron oxide of ferrous-ferric oxide and iron scsquioxide 65? byweight Toluene Rest Phthalic acid resin (specific gravity: l.l2:viscosity: 23.7 stokes (45% nonvolatilc resin part dissolved in tolueneat 25C): ht trade name: Vehicle of paint TAIKO MARINE") 40% by weightManganese dioxide l/( by weight Lead oxide 20); by weight Xylene RestStyrol resin (specific gravity:

l.5: viscosity: 4.3 stokes (25% toluene solution at 25C): trade name (2)Styron 66b) 40% by weight Manganese dioxide l9; by weight Titanium oxide209'? by weight Copper sulfide I'll by weight y ne Rest Cyclized rubber(specific gravity: 1.06: viscosity: 4.] stokes (2571 toluene solution at25C): trade name: THERMOLlTE P) 20% by weight d) Manganese dioxide l4'/(by weight Iron oxide (the same as in a)) 6'71 by weight Ebonite powder(25.47: S) 10% by weight Xylene Rest Rubber chloride (specific gravity:1.6: viscosity: 3.6 stokes (2571 toluene solution at 2ST]; trade name:ALLOPRENE R 2591 by weight e) Manganese dioxide 1071 by weight Copperoxide 20% by weight Plasticizer (DOP: di-t Z-ethylhexyl phthalatel) 5'1by weight Xylene Rest painted respectively with the said solutions (a).(b).

(c). (d) and (e) by air-spraying. They were then natu rally dried toform floating rust preventing films of a thickness of p..

The five samples thus coated with the respective floating rustpreventing films were exposed out of doors. A photograph of the state ofthe surface treated with the treating solution ((1) after the lapse ofabout 15 months is shown in FIG. 3. As evident from FIG. 3, it isunderstood that. in about 15 months. the floating rust preventing filmpeels off and a blackish brown stable rust is formed beneath the saidfilm.

The photograph in FIG. 4 shows the state of the surface treated with thetreating solution (a) after the lapse of about 18 months. As evidentfrom the same photograph. it is understood that a dark brown stable rustis formed in place of the floating rust preventing film.

Further. the samples also treated with solutions (b), (c). (d) and (e)show the same favorable results. though some differences are found inthe time when the stable rusts were formed on the steel surface groundsand in the appearance of the obtained stable rusts.

The thus obtained stable rusts on the steel surface grounds are allstabilized compact films and do not produce any floating rust. eventhough they are continuously exposed out of doors. Therefore there isfound no staining of the surroundings at all. Also. the corrosion of thesteels is very slight.

As detailed in the above. according to the present invention. thesurface of a weatherproof low alloy steel is subjected to a specialcoating treatment so that the penetration of water into the steelsurface ground may be restricted to a minimum. while the permeation ofoxygen may be positively effected, whereby the formation of stable ruston the steel surface ground below the film may be accelerated during thelife of the film. Moreover. the formed rust is made stable by thatportion ofthe oxide pigment (contained in the floating rust preventingfilm) which is incorporated into the stable rust. The net result is thatthe formation of the stable rust prevents the formation of theundesirable floating rust.

As a result of the above phenomenon. the staining of the surroundings ofbuildings and structures made of weatherproof low alloy steel iseliminated. the consumption of the steel materials by corrosion isreduced. and the life of the steel is greatly increased.

What we claim is:

l. A weatherproof low alloy steel member to be used as a material forbuildings and structures. the surface of which is covered with a filmfor accelerating the formation of a compact and stable rust on thesurface of said steel. while preventing the formation of floating ruston the surface of the steel while said stable rust is being formed. saidfilm consisting essentially of at least 1% manganese dioxide; 30-70% ofan oxide pigment, or a mixture of oxide pigments. including saidmanganese dioxide; 0.05 to 10% sulfur; and the rest being an organicfilm forming component selected from the group consisting of an acrylicresin. an alkyd resin. a

consisting of iron oxide. copper oxide. titanium oxide.

and lead oxide.

4. The weatherproof low alloy steel member according to claim I in whichsaid film on the surface of the steel has a thickness of 15 to u.

5. The weatherproof low alloy steel member according to claim 1 in whichthe film contains 0.1 to 5.0% of sulfur.

1. A WEATHERPROOF LOW ALLOY STEEL MEMBER TO BE USED AS A MATERIAL FOR BUILDING AND STRUCTURES, THE SURFACE OF WHICH IS COVERED WITH A FILM FOR ACCELERATING THE FORMATION OF A COMPACT AND STABLE RUST ON THE SURFACE OF SAID STEEL, WHILE PREVENTING THE FORMATION OF FLOATING RUST ON THE SURFACE OF THE STEEL WHILE SAID STABLE RUST IS BEING FORMED, SAID FILM CONSISTING ESSENTIALLY OF AT LEAST 1% MANGANESE DIOXIDE; 30-70% OF AN OXIDE PIGMWENT, OR A MIXTURE OF OXIDE PIGMENTS, INCLUDING SAID MANGANESE DIOXIDE; 0.05 TO 10% SULFUR; AND THE REST BEING AN ORGANIC FILM FORMING COMPONENT SELECTED FROM THE GROUP CONSISTING OF AN ACRYLIC RESIN, AN ALKYD RESIN, A PHTHALIC ACID ESTER RESIN, A POLYESTYRENE RESIN, A CUMARONE RESIN, A CYCLIZED RUBBER AND A RUBBER CHLORIDE.
 2. The weatherproof low alloy steel member according to claim 1 wherein the oxide pigment in the organic film is composed only of manganese dioxide.
 3. The weatherproof low alloy steel member according to claim 1 containing at least one pigment oxide other than manganese dioxide selected from the group consisting of iron oxide, copper oxide, titanium oxide, and lead oxide.
 4. The weatherproof low alloy steel member according to claim 1 in which said film on the surface of the steel has a thickness of 15 to 70 Mu .
 5. The weatherproof low alloy steel member according to claim 1 in which the film contains 0.1 to 5.0% of sulfur. 